Bromine extraction



March 2o, 1945. l `J, J GREBE TAL 2,371,886

ROMINE EXTRACTION Filed Jun'e 4, 1942 2 Sheets-Sheet l A #Cf v Y ngz March 20, 1945.

J. J. GREBE E-r AL BROMINE EXTRACTION 2 Sheets-snee; 2

Filed June 4, 1942 QQ Qboww N MM. M

PatenteclMar. ,20, 1945 anon/EINE ExTnAc'rIoN John J. Grobe, William C. Bauman. and Harold A. Robinson, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application June f1, 1942, Serial No. 445,706

Claims.- (Cl.l .Z3-217) The invention relates to a method of extracting and recovering bromide or iodine in elemental form from solutions containing these halogens in combined form and is more particular-ly useful in connection with a process for the extraction and recovery of these elements from solutions containing the same as halogen.

acids, such as the recovery ofbromine from hydrobromic acid obtained in one phase during the processing of sea Water.

A method.now having extensive commercial application for the extraction of bromine from sea water 'consists in acidifying the sea water and thereafter chlorinating the acidied solution to release the bromine in elemental form. The solution is then blown with air in a suitable tower whereby the bromine is carried oil' in the air stream. Since the bromine in the air stream is very dilute 4it is difdcult lin practice to absorb it directly and therefore recourse is had to a concentrating operation. This operation consists in passing the bromine laden air, sulfur dioxide, and water through a suitable tower under conditions such that chemical reaction occurs and an aqueous solutioncontaining sulfuric acid and hydrobromic acid forms wherein the bromine occurs in combined form in a much higher concentration than in the original saline being proc essed. This solution is then chlorinatedand the bromine steamed out after which the bromine is condensed directly. The process outlined above is'disclosed in greater detail in U. S. Patent The foregoing process -is highly satisfactory from a, commercial standpoint providing a source y The principal object of the invention is, 'there-1 fore. to provide a new method for the liberationV vand extraction of bromine from aqueous acid solutions of hydrogen bromide such' as are obtained in some phases of the process when sea water is being treated for the -recovery of bromine.

Another object is to provide a method for the extraction of bromine and iodine from solutions .containing these elements as halogen acids.

.Other objects and advantages will :be apparent as the description ofthe invention proceeds. We have found that bromine and iodine may' be liberated from suitable concentrations of sulfurie acid containing these halogen acidsby con trolled reaction with nitric acid which is converted to nitric oxide by the reaction. At the same time the nitric oxide so formed can be reconvertedinto nitric acid for re-use by the direct action of air or oxygen and water so that in effect air or oxygen indirectly acts. as the oxidizing agent to effect oxidation of the hydrobromic acid. The reactions forminglthe basis of the present improved process occur in accordance with the following equations which will be referred to hereinafter in the description at the stage of the process at which they occur.

'I'he invention then resides the method hereinafter more fully described and particularly called for by the claims, reference being had to the accompanying drawings wherein Fig. 1 shows diagrammatically in flow sheet form one embodiment of the invention as applied to the extraction of bromine from sea water employing air in the reaction wherein the nitrogen oxides are converted into nitric acid.

1 Fig. 2 is a owsheet sheet similar to that shown in Fig. 1l modied, however, in several steps due to the employment of oxygen in the reaction in which the nitrogen oxides are converted to nitric acid. The invention will be described with reference to processing seawater wherein it is desirable y for economic reasons to iirst free the bromine with chlorine and thereafter absorb the bromine from the air stream to form hydrobromic acid.

In the embodiment shown in Fig. 1 the sea water is acidied at l by acid drawn from `source y 2 and made during a. later stage of the process in a manner to be described below. The acidied sea water is thereafter intimately contacted stream carrying' the bromine is intimately contac-ted 4at 6 with sulfur dioxide and thereafter conducted into thebottom of a suitably paclredv -tower 'l wherein it is'contacted with water 8 'introduced into the top of the tower 1. Chemi-A cal reaction occurs and the bromine is reduced to hydrobromic acid with the attendant formation of sulfuric acid, both of which dissolve in the water solution and ow out the bottom of tower 1. 4At the same time additional sulfuric acid 8 from source l2 -is introduced into tower 'I along with the water, an amount being used such as will produce a sulfuric acid solution of 5 to 20 per cent and preferably about 15 per cent concentration. The acid solution containing the dissolved hydrobromic acid is maintained at a temperature of 25 C. or preferably slightly below this temperature and conducted to a small tower I wherein it meets an upwardly fiowing stream of gas consisting of nitric oxide (NO), nitrosyl bromide (N OBr), and bromine (Brz) introduced into the bottom of tower I0 at II and produced l in a step of the process to be later described.

The nitrosyl bromide in the gas mixture is decomposed by the action of the ldownwardly flow.- ing acid solution into nitricv oxide, nitric acid. and hydrobromic acid (see Equations 2 and 3). This hydrobromic acid along with the original hydrobromic acid and a small amount of free bromine in the gas mixture is dissolved in the downwardly flowing acid solution'while the nitric oxide passes out of tower IIJ at I2. The solution containing dissolved therein sulfuric acid, nitric acid, a small amount of bromine and hydrobromic acid is conducted through a suitably trapped pipe I3 to the toprof tower or still I4, preferably of the bubble cap type. At the same time nitric acid is introduced into the still I 4 and may be suitably added to the process through trapped pipe I3 at I5. The nitric acid place at a temperature between about 50 and 110 C. The freed bromine issteamed out by introducing steam into the bottom of tower I4 at I6 in an amount to maintain the temperature of still I4 at 1,00" to 110 C., 105 C. Ybeing preferred. The amount of nitric acid added to tower still Il is considerably above that theoretically necessary to oxidize the hydrolbromic acid and liberate the bromine for a purpose to be explained below and is preferably in the neighborhood of from 300 to 350 per cent of the theoretical. At the same time complete oxidation is not obtained by use of nitric acid alone, it being in the neighborhood of only 90 per cent. Therefore `a small amount of `chlorine, roughly about 10 per. cent of that theoretically necessary to completely oxidize the HBr, is added to still I4 at a convenient point such as about one third the way up the tower at I1. The chlorine acts as the clean-up oxidant and thus prevents loss of #bromine inthe efliuent. The` gases liberated in the oxidizing and steaming-out tower I4 escape from the tower at I8 and consist of a mixture of bromine, nitrosyl bromide,- and nitric oxide, the latter being present'due to the limitedv dissoci ation of nitrosyl bromide into nitric oxide and V bromine vapor. The gas mixture is led into a continuous bromine recovery still I9 at a point 20 about the middle of. the tower. The temperature of still I ls controlled rather closely so that the temperature at the bottom of the tower is maintained at the boiling point of bromine (59 C.) The gases are thus reuxed in still I9 and a. large portion'of the bromine cornes out at the bottom of the s'tiil through trapped pipe 2l where it may be collected and suitably packaged for commerce. trosyl bromide together with a small amount of bromine are carried out the top of still I9 and into tower I0 where the nitrosyl bromide is decomposed with the formation of nitric oxide, nitric acid, and hydrobromic acid, in accordance with Equations 2 and 3 combined. In addition, a small amount of hydrochloric acid 'is produced corresponding to the chlorine used in the oxidation. As heretofore explained the hydrobromic acid, bromine, and nitric acid are dissolved while the nitric oxide passes from tower I0 through line I2 and is utilizedin a later step in the process as willv be explained below. The solution iiowing from the bottom of still I4 is led through a trapped pipe 22 to a small tower 23 and consists ofa mixture of sulfuric acid and unreacted nitric acid together with a minor proportion of hydrochloric acid. The large excess of nitric acid over that theoretically necesessary employed as mentioned above in the oxidation of the hydrobromic acid solution in tower .I4 is now utilized for converting sulfur dioxide quirements for acidifying the abrine and producing the necessary and desired concentration of acid in tower fl. At the same timelthe amount of nitric acid entering tower 23 through line 22 should of course be sumcient to convert all the sulfur dioxide to sulfuric acid. The acid mixturel consisting mainly of., sulfuric acid with a minor amount of hydrochloric acid is led from the bottom of tower 23 and is divided at 2, a

portion being used to acidity the sea water at I while some of it is led to 'tower 'I to produce the proper acidity of the hydrobromic acid solution. Itl will be noted that the nitric acid entering tower 23 is converted to nitric oxide by the addition of sulfur dioxide to tower 23. This nitric oxide is combined with the nitric oxide issuing out of tower I0 through line I2 at 25. Air is also added at 25 together with a small additional amount of make-up nitrogen dioxide lost out of tower 23 so that the necessary amount of nitric acid win be produced for the oxidizingv steps in towers I4 and 23 in accordance with the reactions illustrated by Equations l and 4.

The mixture of nitric oxide, nitrogen dioxide, and

. air is led into the bottomA of tower 26 while water is introduced at the top of the tower atl 21. The amount oi?l water is controlled so as to produce an acid of concentrated nature (about 60 per cent). The acid so formed is conducted to tower Il and as previously mentioned is introduced into the tower through trapped line I5 where it effects' oxidation of the hydrobromic acid, thus liberating the bromine. i

In the modiiication shown in Fig. 2 wherein oxygen is employed in the conversion o f the nitrogen oxides to nitric acid instead of air it will be noted that the process is exactly the same up to the point where the hydrobromic acid-sulfuric acid mixture is introduced into tower I0. When Oxygen instead of air is employed it is preferably introduced into tower Il i at a point 28 above the point of introduction of the chlorine although it may be added at any point in or after tower Il prior to leading the gases through line I8 to still I9.' The majority of the bromine is separated out in still I9 as a The nitric oxide and ni- 4 amount of chlorine.

i 2,371,886 v I9 and in this case consist of a mixture of nitric oxide, a small amount of bromine vapor, nitrosyl bromide, and oxygen. This mixture is combined` with the nitrogen oxides issuing out of tower 23 at 29 resulting from the reduction of the nitric acid by the sulfur dioxide. To this mixture is added the desired-amount of make-up nitrogen dioxide as at 30 and the mixture is led into tower Ill at Il. In this'case the oxides are readily converted to nitric acid in tower I while waste gases are allowed to escape at vent 3| at the top of "the tower. The nitric acid thenl flows into tower M from tower l0 through line I3. This process eliminates the necessity. of employing a separate nitric 'acid tower 26 and gas mixing chamber 25 as is the case when air is employed as shown in Fig. l. The modifications oi Fig. 2 are possible because when oxygen is employed the nitrogen oxides can be converted in tower I Il without attendant loss due to the large, volume of inerts necessarily present in case air is employed, which would act to carri off the bromine in the vent gas.

In the process described above an amount of sulfur dioxide is employed for reaction with ntric acid such as will furnish the entire acid requirements of the process. Itwill be understood. however, thatthe necessary amount of acid may be added directly as sulfuric acid, in which 4case it is unnecessary to employ such a large excess cf nitric acid in order to have enough nitric acid available for conversion of sulfur dioxide to sulfuric acid to meet the acid requirements of the process. Actually inthe case of bromine it is only necessary that the ratio of nitric acid to bromine, based on the weight of each, be abo'i'e about 0.26 in order that the oxidationbe efiiciently effected. Thus in-/case acidis added clirectly it is only necessary toi employ slightly more nitric acid than is theoretically-necessary, e. g. 130 per cent of theoretical. If the acid is added directly Without recourse to converting'sulfur doxide to sulfuric acid the excess nitric acid may be combined .with the other acid values for acidification purposes or, preferably, only enough sulmentor theprocess. At the same time the nitrogen oxides formed by the action of the nitric acid onthensulfur dioxide and the hydrobromic acid are readily reconverted to nitric acid by the action of air or oxygen and.-water so that it is unnecessary to continually renew the oxidizing agent.

Since itis necessary to add acid to the process in any case the-sulfur dioxide which is reacted with the nitric acid furnishes an exceedingly cheap source of acid and it is only necessary to add slight' amounts of nitrogen oxides to the process as these are lost due to ineicient reconversion. Thus air or oxygen acts indirectly as the oxidizing agent and isthe only oxidizing agent that must be added in quantity once the hydrobroxnic acid is obtained. It will be readily` appreciated that marked economy is effected by i employing air oroxygen as an oxidizing agent in such` avmanner that the principal oxidizing agent is regenerated and continuously recycled.

The invention is similarly applicable to the extraction of iodine from salines containing the same in combined form or to the processing of .various solutions of hydriodic acid, it being necessary to modify the process only slightly in view lof the properties of the iodine.

In the case of iodine recovery the hydriodic acid-sulfuric acid solution produced by adding sulfur dioxide to the iodine-containing air stream is contacted in the steaming-out and oxidizing tower with nitric acid,v The separation of the liberated iodine and oxides of nitrogen may be brought about by collecting them in a suitable tower.. maintained at a temperature slightly above the melting point of the iodine whereby the iodine may be drawn off from a liquid layer separating at the botfur dioxide will be employed to convert the excess nitric acid to nitric oxide.

Although the method has been .described with particular reference to the sea water-bromine process wherein sulfur dioxidel is employed Ito convert the bromine in the blowing out air stream to hydrobromic acid, it will be understood that the method is applicable to process'ng any hydrobromic acid solution c-f suitable' concentration.

employing the method inpconnection with the sea.

water-bromine process outlined above wherein the concentration of the hydrobromic acid produced in one step of the process averagesabout 'I per centit has been. found that the nitric acid oxidizes about90 per cent of the bromine, The

remainder is readily converted by the theoretical- Thus in those instances where chiorinejs not readily available or must i be shipped in from considerable distances a notable saving in the chlorine requirements is effected and hence the economy of the process markedly improved. By the foregoing method the nitric acid acts to oxidize the hydrobromic acid and convert an amount of sulfur dioxide to sulfuric acid such as "will meet thel entire acid requiretom of the tower While the oxides of nitrogen aresuitably collected Aas they issue out of the top of the tower.

We claim:

1,'In a method of recovering bromine in elemental form from hydrobromic acid solutions containing the same, the steps which consist in adding thereto sulfuric acid in amount such that the resulting `concentration of sulfuric acid in the solution is between about 5 and'20 per cent by weight, causing said solution to intimately contact nitric acid present in an amount such that the` ratio of nitric acid to bromine, calculatedas-elemental bromine, is above about 0.26, adding chlorine to complete the liberation of the bromine, heating the solution obtained to a temperature sufficient to vaporize the liberated the vaporized ybromine.

2.In a method of recovering bromine in elef mental form from solutions of hydrobromic acid. the steps which consist in adding sulfuric acid to the solution in an amount such that the. concentration of sulfuric acid in the solution is between bromine and thereafter collecting and condensing about 5 to 20 per cent by weight, bringing nitric acid into intimatel contact with said solution in an amount above about 30,04 per cent oi' that theoretically necessary to liberate the bromine as elemental bromine with the formation of ni i trosyl bromide while maintaining. thetemperature between about ,to 105 C.; adding chlo- `rine Ito complete the oxidation of the hydrobromic acid into bromine, steaming out the bro-f mine, 'separating the bromine fromthe nitrosyl^y bromide bycondensing said bromine, collectingy i oxide is converted into sulfuric acid for use in acidifying operations in the process, collecting the nitrosyl bromide and converting the same into nitric acid by reacting it with air and water, and returning the nitric acid so formed to the voxidizing steps of the process.

3. In a method of recovering bromine in elemental form from seal water, the stepsV which comprise acidifying said sea water, chlorinating the acidiiied sea waterto liberate the bromine, blowing` out the liberated bromine with air, adding sulfur dioxide and Water whereby the brosulfur dioxide an amount of sulfuric acid will f be formed which will meet the acid requirements of acidifying the sea water and bringing the hydrobromic acid solution to the desired sulfuric acid concentration, adding chlorine to complete the liberation of the bromine from the hydrobromic acid solution, steaming out the bromine as a vapor in admixture with the nitrogen oxides formed in the oxidation step, separating the bromine from the nitrogen oxides by condensing the bromine, collecting the aforementioned excess nitric acid and reacting it with sulfur dioxide so as to produce sulfuric acid and nitric oxide, collecting the nitrogen oxides formed in the process and reconverting said oxides to nitric acid by reaction with air and water, and returning the nitric acid so formed to the oxidizing steps of the process.

4. In a method of recovering bromine in elemental form from solutions of hydrobromlc acid, the steps which consist in: adding sulfuric acid to the solution in an amount such' that the concentration of sulfuric acid in the solution is between about 5 to 20 per cent by weight; bringing nitric acid into intimate contact with said solution in an amount such that the ratio by weight of nitric acid to bromine, calculated as maintaining the temperature of solutions between 50-105 C. so as to oxidize nearly all the hydrowater; treating the mixture thus obtained with elemental bromine, is above about 0.26 while,-

bromic acid into bromine and nitrosyl bromide; adding chlorine to complete the oxidation oi the hydrobromic' acid into bromine',- the bromine formed in the oxidation step'being vaporized in admixture with the nitrosyl bromide; separating the bromine from the vapor mixture by condensation; collecting any excess nitric acid from the oxidation stepland reacting it with sulfur dioxide whereby nitric oxide and sulfuric acid areformed; and converting the nitrosyl bromide and the nitric oxide into nitric acid for reuse in the oxidation step..

.5. In a method of recovering bromine ln elemental form from an aqueous hydrobrcmic acid solution, the steps which consist in: adding sulfuric acid to the solution in an amount such that the resulting solution contains between about 5 to 20 per cent by weight; contacting the resulting solution with the mixture formed in the later step of the method of nitrosyl bromide, oxygen, and nitric oxide so as to bring about the presence of nitric acid in the aforesaid resulting solution for oxidizing the hydrobromic acid therein to bromine, said nitric being formed by the 1 interaction of the nitrosyl bromide, oxygen, and

steam, chlorine, and oxygen, the steam raising the temperature of the mixture to between about and 105 C., thereby to induce the nitric acid to oxidize nearly all the hydrobromic acid to bromine and nitrosyl bromide, the chlorine completing the oxidation of the hydrobromic acid, the oxygen being added in an amount suilcient for the nitric acid to be formed in the second step,

and the temperature being suillcient to vaporize the bromine in admixture with the nitrosyl bromide and oxygen; separating the mixed vapors thus produced from the resulting aqueous nitric acid'solution; separating the bromine from the mixed vapors by condensation; treating the aqueous nitric acid solution with sulfur dioxide so as to convert the nitric acid to sulfuric acid and nitric oxide; adding the nitric oxide thus obtained to the mixture containing the nitrosyl bromide and oxygen separated from the bromine in the condensation step; delivering the resulting gaseous mixture to the second step; and delivering at least a portion of the sulfuric acid produced from the nitric acid to the first step.,

JOHN J. GREBE.` mLuAM C. BAUMAN. HAROLD a. ROBINSON. 

